An alkenyl phosphorus compound, for example, an alkenyl phosphonic acid ester or a alkenyl phosphinic acid ester, or an alkenyl phosphine oxide compound is a useful compound as a physiologically active substance, or as a synthetic intermediate for, for example, pharmaceuticals and/or agrochemicals. Further, an alkenyl phosphorus polymer obtained by polymerizing an alkenyl phosphorus compound is useful as a metal extractant, or as a flame retardant.
As a method for synthesizing an alkenyl phosphorus compound, there is a known method comprising reacting a phosphorus compound having an intramolecular P—H bond with an acetylene compound in the presence of a transition metal catalyst, for example a nickel catalyst, which catalyzes a hydrophosphorylation reaction. For example, Patent Literature 1 discloses that, even in a reaction producing a regioisomer, an alkenyl phosphorus compound can be obtained with high regioselectivity by carrying out the above-described reaction in coexistence with of diphenyl phosphinic acid. Further, Patent Literature 2 discloses that, by using a nickel catalyst and an acid which is a hydride donor in combination, a nickel-hydride complex is formed in a reaction system, and thus an amount of a catalyst used can be reduced to about 0.5 mol %.
As described in these Patent Literatures, a method which comprises addition of an acid to a reaction system is effective to increase catalytic activity. However, a ligand of a nickel catalyst used in the reactions of these Patent Literatures is an expensive phosphine, and thus, when one intends to produce an alkenyl phosphorus compound industrially advantageously, it is necessary to further reduce an amount of a nickel catalyst used.
In addition, the methods described in Patent Literatures and 2 are studied in a very-small scale reaction system (in Examples of Patent Literatures 1 and 2, reactions are carried out with a total amount charged in a batch of on the order of several to several tens of grams). Thus, when one intends to apply the methods described in. Patent Literatures 1 and 2 to a larger reaction scale, it has been quite difficult to obtain an alkenyl phosphorus compound in high yield as a consequence of, for example, an influence of contact efficiency between a phosphorus compound as a raw material and an acetylene compound (particularly, a gaseous acetylene compound including acetylene), or catalysis deactivation by heat of reaction. In this respect, for example, Patent Literature 3 discloses that, in a method as described in Patent Literature 2, reaction yield is about 40 to 60% by a batch method, and thus it is difficult to produce an alkenyl phosphorus compound at an industrial scale (see, paragraphs [0074] to [0075]).
Additionally, in the above-described Patent Literature 3, a method for producing an alkenyl phosphorus compound using a microreactor system is proposed as a method by which an alkenyl phosphorus compound can be produced in high yield even at an industrial scale. In a microreactor, since minute quantities of a phosphorus compound and acetylene are reacted in a flow path, deactivation of a catalyst by heat of reaction can be suppressed.
However, since acetylene has low solubility in a reaction solvent, it is necessary to pass a large amount of solvent in order to pass an acetylene solution through a microreactor while gasification is suppressed (in Examples of Patent Literature 3, an amount of solvents used is more than several tens of times as much as production quantities of a vinyl phosphorus compound). Thus, the method requires an unreasonably large solvent storage equipment and separation equipment relative to production quantities, and further a large amount of a catalyst is also used to maintain catalyst concentration, and thus the method is economically extremely unfavorable.